1. Field of the Invention
This invention relates to fluid-operated devices and in particular to hydraulic snubbers and the like adapted for use in a radioactive environment.
2. Description of the Prior Art
In U.S. Letters Pat. No. 3,190,702, of Francis S. Flick, which patent is owned by the assignee hereof, a sealing structure for piston and cylinder devices is illustrated having an improved resilient annular seal including a portion mounted in a bushing recess and another portion engaged by a follower ring which is biased by a wave spring to effect a sealing engagement thereof with an outer surface of a piston rod. Thus, the seal has both a dynamic and a static sealing portion adapted for use in machine tool grade piston and cylinder devices. The bushing is removably secured to the head of the piston and cylinder device by a removable retainer plate so that servicing of the seal may be effected by the axial removal of the retainer plate and bushing together with the seal from the outer end of the piston rod.
The outer end of the piston rod may conventionally have attached thereto other elements, and in the Flick patent, a threaded securing portion is shown at the outer end of the rod. One use of such a device is as a hydraulic snubber in a nuclear power installation wherein the device is disposed in a radioactive environment. In such an environment, nonmetallic seals such as that disclosed in the Flick patent may suffer radiation degradation requiring replacement. One conventional nuclear power installation of such type utilizes a rod eye threadedly connected to the outer end of the piston rod. The rod eye serves as a connector to a tubular or cylindrical element which is extended therethrough after the rod eye is fully threaded onto the piston rod end.
Where it is desired to service the seal of such a device, it has heretofore been necessary to remove the rod eye so as to permit the axial withdrawal of the annular bushing and seal. To permit the unthreading removal of the rod eye, the element extended through the eye must first be withdrawn.
Such snubbers protect the elements connected thereto from excessive loads as may occur in a seismic event relating to the nuclear power equipment. The snubber permits a slow movement of the elements at any time, such as may be caused by differential thermal expansion while yet providing a snubbing action relative to any sudden large force applied thereto. In such nuclear powered installations, it is necessary to assure proper sealing action at all times. A substantial number of such snubbers may be employed in such an installation. The Nuclear Regulatory Commission has promulgated a directive that from and after the time a hydraulic snubber has been determined to be inoperable, continued reactor operation is permissible only during the succeeding 72 hours unless the snubber is sooner made operable. As such snubbers may be relatively large and the elements connected thereto relatively bulky, the 72-hour limit presents a serious problem where the apparatus must be effectively disassembled to permit the replacement of the snubber seal.
Not only is there substantial difficulty involved in such assembly and disassembly of such relatively large hydraulic snubbers, but very often such snubbers are located in relatively inaccessible areas.
Thus, the maintenance of such hydraulic devices in such environments presents a serious problem.